Photo-electric converter

Abstract: An image information processing apparatus comprises a parallel connection circuit for parallelly connecting a plurality of photo-electric conversion elements, a combined signal read circuit for reading out a combined signal from the plurality of parallelly connected photo-electric conversion elements, an individual signal read circuit for reading out an independent individual signal of each of the plurality of photo-electric conversion elements, a photometry circuit connected to the combined signal read circuit and a distance measurement circuit connected to the individual signal read circuit.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a photo-electric converter such as an image sensor used in an image information processing apparatus such as a copying apparatus, facsimile apparatus or a video camera, or an AE/AF sensor of an automatic exposure and/or automatic focusing device of a camera. Related Background Art As electronic technology has advanced recently, high performance of products such as cameras, copying machines and facsimile machines have been attempted. For example, in a single reflex type camera, almost all products are presently equipped with the automatic exposure (AE) function and the automatic focusing (AF) function. In the AE function, an absolute light intensity of the entire area in one frame corresponding to an image pickup area, or a sub-area of a frame area, is measured to automatically control the exposure or the shutter speed. On the other hand, in the AF function, the distance to an object is calculated using a correlation function of an object pattern, to automatically control a lens position. Thus, in order to enhance precision, it is necessary to further subdivide the image pickup area. Because the image pickup areas and the post-processing are different between the AE and the AF, it is necessary to use separate photo-electric converters (sensors). While various improvements have been made in the individual products to reduce the cost, a significant effect has not been attained. In a known photometry sensor used for the AE function, when the light intensity of an entire area is to be detected, signals of respective areas are amplified by logarithmic amplifiers and output signals thereof are multiplexed. In a known distance measurement sensor used for the AF function, emitters of phototransistors for the respective photo-sensing areas are connected in common and a peak signal is measured. With this method it is difficult to measure an absolute light intensity of the entire photo-sensing area and it is not used for the AE function. By way of example, a typical example of the former is described in detail in US-A- 5,115,124 and a typical example of the latter is described in detail in US-A- 4,751,559. In the former method, the signal processing in the succeeding stage and the drive of the decoder to multiplex the signals are complex, and the latter method is not suitable for the AE function. US-A-4908709 proposes a solid state electronic imaging device having a plurality of columns of photodiodes together with a vertical CCD for each column of photodiodes. In order to read out an image signal, charges from the photodiodes are transferred into the CCD's, and these are clocked in a forward direction to transfer the charges to a horizontal CCD for read-out. In one embodiment, light measurement is performed by clocking the vertical CCD's in a reverse direction. The vertical CCD's are divided into groups, and in each group the reverse-clocked signals are transferred onto a common discharge line. Each discharge line is connected to earth through a resistor and is also connected to a respective integration unit. The integration units integrate the signals on the discharge lines and provide light measurement signals for the respective areas defined by the groups of CCD's. The light measurement signals may be used for generating an iris control signal and/or a shutter speed control signal. In another embodiment, light measurement is performed by transferring charges from photodiodes into the sensor substrate instead of transferring them into the CCD's, and the substrate is connected to a charge discharge line which is linked to A/D converter to provide a digital light measurement signal. EP-A- 0 627 847 discloses using transistors as photo-elements, and selectively connecting base terminals thereof for simultaneous reset of plural elements. The transistors may be provided with multiple emitters, one used for individual pixel read-out, another used for detecting peak signals. SUMMARY OF THE INVENTION According to the present invention there is provided photo-electric conversion apparatus as set out in claim 1 and a method of operating photo-electric conversion apparatus as set out in claim 13. The remaining claims set out optional features. An embodiment of the present invention provides a high performance photo-electric converter which permits the variation of the effective area of the photo-sensing area with a simple construction. In accordance with the preferred embodiment, since the plurality of photo-electric conversion elements are connected in parallel, the individual photo-sensing areas may be connected in common to produce the combined signal for the entire photo-sensing area. Other objects and features of the present invention will be apparent from the following description of the embodiments and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a circuit diagram of an embodiment 1 of the present invention, Fig. 2 shows a timing chart for explaining an operation of the converter of the embodiment 1, Fig. 3 shows a timing chart for explaining an operation of the converter of the embodiment 1, Fig. 4 shows a circuit diagram of a converter in accordance with an embodiment 2 of the present invention, Fig. 5 shows a circuit diagram of a converter in accordance with an embodiment 3 of the present invention; Fig. 6 shows an equivalent circuit of one photo-electric conversion element of the converter of the embodiment 3 of the present invention, Fig. 7 shows a sectional view of an example of the photo-electric converter used in the present invention, and Figs. 8A and 8B show block diagrams of an image information processing apparatus which uses the photo-electric converter of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiments, switching elements function as parallel connection means. When the switching elements are turned on the photo-electric conversion elements are connected in parallel and a combined output is produced from an output terminal. On the other hand, when an individual signal is to be derived from one of the photo-electric conversion elements, the switching elements are turned off so that the individual output may be read. The size of the photo-sensing area may be changed by the selective turn on/off of the switching elements. When only one of the switching elements is turned on, a combined signal (mixed signal) of first and second photo-electric conversion elements is produced. Similarly, when only a different one of the switching elements is turned on, a combined signal of the second and a third photo-electric conversion elements is produced. The sensor may be operated in the following operation sequence. First, the switching elements are turned on to produce the signal for the entire photo-sensing area. Then, the switching elements are turned off to produce the signals of the respective photo-electric conversion elements individually. In this manner, the combined signal and the individual signals may be produced. It is preferable to reset (initialize) the photo-electric conversion elements immediately before the second read operation of the signals. The above operation may be controlled by a drive circuit integrated on the same semiconductor substrate or an off-chip drive circuit. The photo-electric conversion elements used in the present invention may include bipolar transistors, junction-type field effect transistors, gate insulated field effect transistors and static induction transistors. The parallel connection means used in the present invention may include transistors and charge coupled devices (CCD's). The read means used in the present invention may be those having resistive loads and those having capacitive load, and may include CCD registers, BBD registers, shift registers or multiplexors as required to reduce the number of output terminals. Specific embodiments of the present invention will now be explained in detail although the present invention is not limited to those specific embodiments but any suitable forms of the present invention may be used. Referring to Fig. 1, a first embodiment of the present invention is explained. In the present embodiment, bipolar photo-electric conversion elements are one-dimensionally arranged as photo-electric conversion elements. Base regions of the respective elements are connected through PMOS transistors M 11 -M 14 . The combined parallel connection output read operation (read mode 1) in the present embodiment is now explained with reference to a timing chart of Fig. 2. During the present operation, a low level voltage is applied to terminals  T and  VC so that emitter terminals of the bipolar transistors B 1 - B 4 are floating. The low level voltage is applied to a terminal  R , the PMOS transistors M 11 - M 14 are turned on, and the base regions of the bipolar transistors B 1 - B 4 are connected in parallel. When the pulse at  BR is raised to a high level at a time t 1 , the NMOS transistor M BR is turned on and the base regions of the bipolar transistors B 1 - B 4 are reset to the reset voltage V BR . When the pulse at  BR falls at a time t 2 , the base regions of the bipolar transistors B 1 - B 4 float while they are connected in common. Accordingly, light directed to the photo-electric converter is photoelectrically converted by the PN junctions formed between bases and collectors of the respective bipolar transistors and the generated electron-hole pairs are accumulated on the base regions so that the potential of the base line 3 of each bipolar transistor rises. When a pulse  ON rises at a time t 3 , an NMOS transistor MA1 is turned on so that a signal amplified by an NMOS transistor MA2 having the base line 3 connected to a gate thereof, and further by an output amplifier 4, is output at an output terminal OUT1. By this operation, the light intensity directed to the entire photo-sensing area is determined, and based on this signal, the exposure may be determined by photometry means, not shown, to conduct the AE operation. In the present embodiment, the photo-carriers are accumulated while the emitter terminals of the bipolar transistors are floating. Alternatively, the accumulation may be made while a high level voltage is applied to  VC to reverse bias the base-emitter junctions. In this case, the photo-electric conversion is also effected in the base-emitter junction areas so that the sensitivity is enhanced. The signal read operation of the individual photo-electric conversion elements (read mode 2) is now explained with reference to a timing chart of Fig. 3. At the time t 1 , the low level pulse is applied to  R to connect the bases of the bipolar transistors B 1 - B 4 in common and at the time t 2 ,  BR rises. The NMOS transistor M BR is turned on and the base regions are reset to the voltage V BR . After the reset, the pulse at  R rises to a middle level at a time t 3 so that the PMOS transistors M 11 - M 14 are turned off and the individual photo-electric conversion elements are disconnected. At a time t 4 , the pulse at  VC rises and the NMOS transistors M 21 - M 24 are turned on and the emitter terminals of the bipolar transistors B 1 - B 4 are biased to V VC . At a time t 5 , the pulse at  R rises to the high level so that the base potentials of the bipolar transistors B 1 - B 4 are raised through capacitors C 1 - C 4 and the base-emitter junctions are forwardly biased. Thus, the bipolar transistors simultaneously operate in the emitter follower operation and the holes on the bases are recombined and the base potentials fall to V VC + V BE (transitional reset). After the transitional reset, the pulse at  R falls to the middle level and the base potentials also fall through the capacitors C 1 - C 4 so that the base-emitter junctions are reversely biased. Thereafter, the accumulation of the photo-carriers starts. After the lapse of a predetermined accumulation time, at a time t 6 , the high level pulse is applied to  T so that the NMOS transistors M 31 - M 34 are turned on. Subsequently at a time t 7 , the high level pulse is applied to  VC so that the NMOS transistors M 21 - M 24 are turned on and the emitter terminals of the bipolar transistors B 1 - B 4 and the capacitors C T1 - C T4 are reset to the voltage V VC . After the reset, the pulse at  VC falls so that the NMOS transistors M 21 - M 24 are turned off and the emitter terminals of the bipolar transistors B 1 - B 4 are floating. At a time t 8 , the pulse at  R rises and the base potentials rise so that the base-emitter junctions are forwardly biased and the photo-carriers accumulated on the bases of the respective photo-electric converting elements are read into the capacitors C T1 - C T4 , respectively. Then, at a time t 9 , the high level pulse is applied to  RES to turn on the NMOS transistor M RS so that the output line 2 is reset and the scan circuit is activated, and the signals are transferred, starting from the signal on C T1 , to the output terminal OUT2 through the output circuits. This output signal undergoes processings such as sample-hold processing and A/D conversion processing by an external circuit, and then correlation operation of each output is performed to be used in operations, for example, the AF operation in which the in-focus position is detected by the distance measurement means not shown. It should be understood that the respective bit signals may be used as one-dimension signal other than the AF operation. Fig. 4 shows a second embodiment of the present invention. The present embodiment is an expansion of the first embodiment in which the photo-electric conversion elements are arranged in two dimensions. In the read mode 1, all of outputs H1 - H4 of a vertical scan circuit 10 are rendered low level so that the photo-electric conversion elements are connected together in rows and the wirings thereof are connected in common by the line 3 and connected to the gate terminal of the NMOS transistor MA2. As a result, an average voltage of the base voltages of all pixels is produced on the line 3 and an amplified signal is produced at the output terminal OUT1. In the read mode 2, a pulse corresponding to  R in the first embodiment is sequentially applied in the sequence of H1 - H4 from the vertical scan circuit and the photo-signals of the respective pixels are time-serially output to the output terminal OUT2. Fig. 5 shows a third embodiment of the present invention. In the present embodiment, compared to the second embodiment of Fig. 4, resetting NMOS transistors MR1 - MR4 and amplifier input stage NMOS transistors MA21 - MA24 are provided for the respective base lines of each row of the photo-electric conversion elements. It intends to improve the detection sensitivity in the read mode 1. This will be briefly explained below by referencing an equivalent circuit of a unit photo-electric conversion element shown in Fig. 6. As shown in Fig. 6, connected to a base region of a bipolar transistor are; C ox capacitance for resetting the photoelectric conversion element and reading a signal C g gate capacitance of a PMOS transistor as well as parasitic capacitances; C bc base-collector junction capacitance, C be base-emitter junction capacitance, C gs gate overlap capacitance of the PMOS transistor A voltage increment ΔV B caused by the irradiation of light is given by; ΔV B = (N x N ph x η x S x q x L x t s )/ {N x (C ox + C g + C bc + C be + C gs )} where N : number of photo-electric conversion elements connected in parallel N ph : number of photons (cm -2 , t -1 , w -1 ) per unit area, unit time, unit photo-energy η : quantum efficiency q : unit charge (C) L : photo-energy (W) t s : accumulation time (sec) Namely, the detection sensitivity (ΔV B ) is independent from the number of photo-electric conversion elements connected. Accordingly, in the present embodiment, the output ΔV B of the elements connected in parallel for each row is output to the input gate of the amplifier comprising the NMOS transistors M A1 , M A2i ( i = 1 - 4) and the outputs thereof are connected in common and supplied to the amplifier 4 to enhance the detection sensitivity. Fig. 7 shows a sectional view of a sensor when a bipolar transistor is used. Numeral 101 denotes an n substrate, numeral 102 denotes an n - epitaxial layer, numeral 101' denotes an ohmic contact layer to a collector electrode 101'', numeral 103 denotes a p base region, numeral 104 denotes an insulation film, numeral 105 denotes a gate electrode, numeral 106 denotes an emitter electrode which is an output terminal connected to an emitter region 108, and numeral 107 denotes an insulation film. By applying a high pulse, a middle pulse or a low pulse to the gate electrode 105, the PMOS transistor having a source and a drain formed by the base regions 103, and functioning as a switching element, is turned on and off. Fig. 8A shows a block diagram of a configuration of an information processing system such as a communication system, a facsimile apparatus, a video recorder, a copying apparatus or a scanner, which uses the photo-electric converter of the present invention. OR denotes a document sheet bearing image information, numeral 601 denotes a focusing lens and numeral 602 denotes a photo-electric converter embodying the present invention. The photo-electric converter may be a line sensor for the facsimile apparatus, and an area sensor for the video recorder. Numeral 603 denotes a control circuit including a central processing unit and it is connected to the photo-electric converter 602 through an output line 610 for driving the photo-electric converter and a power supply line 611, and selects one of the two read modes. Numeral 604 denotes a record control circuit which is connected to a recording head 605 to write information on a recording medium 606. The recording head 605 may be a magnetic head for the video recorder and a thermal head or an ink jet head for the facsimile apparatus. The recording head 605 may be substituted by a recording unit located at a different site through a cable for the communication system. The photo-electric conversion element of the present invention may be used in the photometry mode to determine whether a document sheet is placed on a document sheet table. Depending on the detection result (the presence or absence of the document sheet), the power supply is turned on or off to save the power consumption. Further, the read operation may be started after the detection of the document sheet. In detecting the presence or absence of the document sheet, a weak LED light is flashed and directed to the document sheet, and if a signal is sensed by a sensor in the photometry mode in synchronism with the flashing the presence of the document sheet is detected. When the document sheet is not present, the signal is not produced by the sensor in the photometry mode and the absence of the document sheet is detected based thereon. It is preferable to apply an anti-reflection coating to a cover surface of the document sheet table to prevent the LED light from being reflected by the cover surface of the document sheet table which faces the document sheet and the reflected light from being directed to the sensor. The present invention is suitably applicable to the information processing system described above. When it is applied to an image pickup apparatus such as a camera, the combined signal may be supplied to photometry means 620 as shown in Fig. 8B so that the exposure in picking up the image is determined and the diaphragm and shutter speed are determined based on the exposure. The individual signals may be applied to the distance measurement means 621 to detect the in-focus position. The photometry means and the distance measurement means are connected to the photo-electric converter and process the output signal therefrom. One of a mode to read the individual signal of each photo-electric conversion element and a mode to read a combined (mixed) signal of the plurality of photo-electric conversion elements is selected by a control circuit 603 to produce a desired signal. In accordance with the present embodiments, the size of the photo-sensing area can be switched with a simple construction and a compact photoelectric converter with a high performance is provided at a low cost.

Claims: A photo-electric conversion apparatus comprising: a plurality of photo-electric conversion elements (B 1 , B 2 , B 3 , B 4 ) for generating photo-signals by photo-electric conversion; connection means (M 11 , M 12 , M 13 , M 14 ) for connecting at least some of the photo-electric conversion elements to provide a combined photo-signal therefrom; and combined signal read means (3, MA2, 4)for reading out the said combined signal, wherein the photo-electric conversion elements each comprise a transistor for amplifying photo-signals present at its input and providing the amplified signals at its output, and the connection means connects the photo-electric conversion elements on the input side of the transistors to provide said combined photo-signal. A photo-electric conversion apparatus according to claim 1 wherein connection by said connection means results in an average output of the photo-signals of the photo-electric conversion elements which are connected. A photo-electric conversion apparatus according to claim 1 or claim 2 further comprising individual signal read means (M 31 , M 32 , M 33 , M 34 , 1, 2, 5) for reading out an independent individual said amplified signal from the output side of the said transistor of each of the plurality of photo-electric conversion elements. A photo-electric conversion apparatus according to any one of the preceding claims comprising a control means (10) for selectively controlling the connection means to connect two or more of the photo-electric conversion elements during a storage or a read-out operation thereby to provide the said combined signal and for selectively controlling the connection means to disconnect thereby to permit separate amplified outputs from separate said photo-electric conversion elements. A photo-electric conversion apparatus according to any one of the preceding claims wherein the transistor is a bipolar transistor. A photo-electric conversion apparatus according to any one of claims 1 to 4 wherein the transistor is a junction-type field effect transistor. A photo-electric conversion apparatus according to any one of claims 1 to 4 wherein the transistor is an insulated gate field effect transistor. A photo-electric conversion apparatus according to any one of claims 1 to 4 wherein the transistor is a static induction transistor. An image information processing apparatus comprising a photo-electric conversion apparatus according to claim 3; photometry means (620) connected to said combined signal read means (4); and distance measurement means (621) connected to said individual signal read means (5). An image information processing apparatus comprising a photo-electric conversion apparatus according to any one of claims 1 to 8 and a light source. An image information processing apparatus comprising a photo-electric conversion apparatus according to any one of claims 1 to 8 and means (604, 605) for recording an image signal from the photo-electric converter on a recording medium (606). A camera having an automatic exposure system including a photo-electric conversion apparatus according to any one of claims 1 to 8. A method of operating a photo-electric conversion apparatus comprising a plurality of photo-electric conversion elements for accumulating photo-signals generated by photo-electric conversion and connection means for selectively connecting or disconnecting the photo-electric elements, the method comprising connecting two or more of said photo-electric conversion elements during or after the accumulation of the photo-signals so as to provide a combined output from the connected photo-electric conversion elements, wherein each said photo-electric conversion element comprises a transistor for amplifying photo-signals present at its input and providing the amplified signals at its output, and the connection means connects the photo-electric conversion elements on the input side of the transistors to provide said combined output.

Inventors: MIYAWAKI MAMORU, UENO ISAMU, MIYAWAKI, MAMORU, UENO, ISAMU, MIYAWAKI, MAMORU, C/O CANON KABUSHIKI KAISHA, UENO, ISAMU, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1994
Main classification: H04N3
IPC codes: H04N3, H04N1, H04N5